The present invention relates to a method and a device for obtaining a data of tape thinness and/or hub radius of a tape reel. The obtained data is used for the purpose of calculation so as to obtain an amount of running time of a tape and residual playing or recording time of a tape such as a tape recorder, digital audio tape recorder and video tape recorder and the like.
In this kind of a device for detecting an amount of running time of a tape and an amount remaining on a tape and for the purpose of displaying elapsed time and residual time of a tape, it is conventionally known that a period of a pulse string (hereinafter referred to as reel pulse) obtained corresponding to the rotation of a tape reel in a take-up side or a supply side is measured, then the measured period is converted to a residual amount of tape by calculation (for example, refer to Japanese Laid-Open Patent Publication Nos. 58-19777, 57-143772, 63-214988, 63-214989 and 63-214990).
In a conventional calculating method, calculation is performed by substituting a constant value for the tape thinness or the hub radius without taken into consideration the tape thinness and the difference of the hub radius of a tape reel in a device. However, the value of tape thinness or hub radius is actually different from the other in response to the different kinds of tapes or manufacturing companies. Further, when a tape capable of long time recording is required in the future, it is necessary to make the hub radius smaller. In this case, erroneous data is output when tapes having different radius of hubs are used, thus an erroneous data of residual time of the tape is displayed. Further, a precise control of the tape velocity not for injuring the tape at the end part of the tape cannot be attained.
It is known that hardware is set to deal with the above problem corresponding to the difference of tape thinness. For example, in a digital audio tape recorder, there is provided a detecting sensor for detecting what kind of tape is used through a hole provided on a tape case. Based on the detected result, the value used for calculation is changed. Further, it is known that a changeover switch operated by a user corresponding to the kind of tapes is provided in a video tape recorder.
However, it may be difficult to correspond practically to many kinds of tapes having different thinness. Further, in the above video tape recorder providing the changeover switch, when the user sets the switch at the erroneous position, erroneous data is displayed.